errors: improve formatList in errors.js

benchmark/error/format-list.js

@@ -0,0 +1,29 @@
+'use strict';
+
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  n: [1e7],
+}, {
+  flags: ['--expose-internals'],
+});
+
+const lists = [
+    [],
+    ['a'],
+    ['a', 'b'],
+    ['a', 'b', 'c'],
+  ];
+
+function main({ n }) {
+  const {
+    formatList
+  } = require('internal/errors');
+
+  bench.start();
+  for (let i = 0; i < n; ++i) {
+    for (let j = 0; j < lists.length; ++j)
+    formatList(lists[j]);
+  }
+  bench.end(n);
+}

lib/internal/errors.js

@@ -901,8 +901,13 @@ function determineSpecificType(value) {
  * @returns {string}
  */
 function formatList(array, type = 'and') {
-  return array.length < 3 ? ArrayPrototypeJoin(array, ` ${type} `) :
-    `${ArrayPrototypeJoin(ArrayPrototypeSlice(array, 0, -1), ', ')}, ${type} ${array[array.length - 1]}`;
+  switch (array.length) {
+    case 0: return '';
+    case 1: return array[0];
+    case 2: return `${array[0]} ${type} ${array[1]}`;
+    default:
+      return `${ArrayPrototypeJoin(ArrayPrototypeSlice(array, 0, -1), ', ')}, ${type} ${array[array.length - 1]}`;
+  }
 }
 
 module.exports = {